The present invention relates to an adaptive control device and a shaking table and in particular to an adaptive control device for controlling the shaking table system so that a response from a process to be controlled is matched with a target and to a shaking table using the device.
The adaptive control is a control method for adaptively changing a control parameters in real time so as to achieve a desired input-output characteristics even when dynamic characteristics of the process to be controlled are changed by operating conditions and an environment. As such a control method, there is a method which identifies the process to be controlled in real time and the identification result is used to determine control coefficients of an adaptive filter so as to modify an input signal to the process to be controlled in real time or a method which creates a filter in real time to agree a response signal from the process to be controlled with a desired response signal, so that an adaptive filter having the same characteristics as this filter is used for real-time modification of an input signal to the process to be controlled. These control methods have been used mostly for control process having a large time constant such as a liquid or a flow rate control in chemical plants.
There are also attempts to use these methods for compensating the transfer characteristic fluctuation of a shaking table on which an object to be tested is loaded (for example, Ide et al xe2x80x9cControl of Electro-hydraulic Shaking Tablesxe2x80x9d The Japan Society of Mechanical Engineers, Dynamics and Design Conference 1999, Proceeding Vol. B (1999), pp. 15-18, and Maekawa et al xe2x80x9cAdvanced Control of Three-dimensional Shaking Table, 1st Symposium on the Improvement of seismic disasters based on the structure crash process analysis, Proceeding (2000-3), pp. 51-54). Here, the shaking table is one of the seismic test devices. FIG. 2 shows a configuration example thereof. In FIG. 2, a table 6 is supported on a basement 121 via a bearing 120. The bearing is not necessarily required depending on the configuration of the shaking table. The table 6 is connected to an actuator 5 mounted on the basement 121. Moreover, shaking table state measurement means 122 is set on the table 6. The actuator 5 is controlled by a feedback controller 4 using as feedback signals shaking table state variables measured by the shaking table state measurement means 122. A specimen 3 loaded on the table 6 is excited, for example, by seismic acceleration, so that its behavior is observed and structual reliability is evaluated. In case of a shaking table control, the upper limit of the control frequency range is, for example, 50 Hz or above. That is, the time constant is small as compared with chemical plants.
FIG. 3 is a block diagram of an example of the shaking table control system using an adaptive control. A controlled object 1 includes a shaking table 2 and a specimen 3. The shaking table 2 includes a feedback controller 4, an actuator 5, and a table 6. Identification means 15 includes a digital filter 10, a subtractor 16, and adaptive means 14. A command signal 101 generated by a signal generator 7 is modified into a modified command signal 102 by an adaptive filter 8 and fed to the feedback controller 4. The feedback controller performs PID compensation and feedback compensation and generates a drive signal 103. The drive signal 103 is fed to the actuator 5 so as to excite the table 6 and the specimen 3 loaded on this table. Here, a reaction force from the specimen 3 is added to the table and as a result, the shaking table transfer characteristics fluctuate. To solve this problem, the subtractor 16 is used to determine an estimated error 108 of a signal 107 obtained by supplying an actual shaking table response signal 106 to the digital filter 10 against a desired shaking table response signal 105 obtained by supplying the modified command signal 102 to a reference signal generator 9. In order to minimize this error, the adaptive means 14 determines by control coefficient 109 of the digital filter 10 using, for example, the least mean square (LMS) method in real time, and the fluctuation of the shaking table transfer characteristic due to the specimen is compensated by matching the characteristics of the adaptive filter 8 to the characteristics of the digital filter 10.
In the aforementioned example of the shaking table control, it is known that when the order of the digital filter 10 is not sufficiently higher than the order of the adaptive filter 8 required for compensation, identification cannot be performed because of the effect of noise contained in the shaking table response signal 106 and the effect of the higher-order vibration mode of the specimen and the shaking table itself other than for the compensation. Therefore, it is necessary to determine a control coefficient for a higher-order digital filter 10, which requires a very long time such as 5 minutes for calculation. This causes a problem that the identification cannot be performed for an earthquake wave which lasts only for several seconds for several tens of seconds.
It is therefore an object of the present invention to provide an adaptive control apparatus capable of compensating only a desired frequency band and significantly reducing the time required for identifying a process to be controlled, and a shaking table capable of real-time compensation of the shaking table transfer characteristic fluctuation by a specimen or the like.
The present invention provides a shaking table including:
a table to load a specimen;
actuators to excite the table;
a feedback controller for generating a drive signal for the actuator so that an inputted second command signal is agreed with a response signal indicating a vibration state of the table having the same dimension as this second command signal;
an adaptive filter having variable filter coefficient which is supplied with an external first command signal indicating a target value of the response signal and generates the second command signal so as to compensate the transfer characteristics from the feedback controller to the table loading the specimen;
a mask signal generator for generating a mask signal having no frequency component in the frequency band compensated by the adaptive filter;
a first adder for adding the mark signal to the second command signal; and
a second adder for adding the mask signal to the response signal;
an identification unit which is supplied with the outputs of the first and the second adders for calculating the filter coefficients of the adaptive filter for compensating the transfer characteristic and supplying the calculated coefficient to the adaptive filter.
Moreover, the present invention provides a shaking table includes:
a table for loading a specimen;
a actuator for actuating the table;
a feedback controller for generating a drive signal for the actuator so that an inputted second command signal is agreed with a response signal indicating a vibration state of the table having the same dimension as this second command signal;
an adaptive filter having variable filter coefficients which is supplied with an external first command signal indicating a target value of the response signal and generates the second command signal so as to compensate the transfer characteristics from the feedback controller to the table loading the specimen;
a mask signal generator for generating a mask signal having no frequency component in the frequency band to be compensated by the adaptive filter;
a reference signal generator which is supplied with the second command signal and calculates the target value of the response signal using a desired transfer characteristics or a transfer characteristics of a predetermined non-load state;
a first adder for adding the mask signal to an output signal from the reference signal generator; and
a second adder for adding the mask signal to the response signal;
an identification unit which is supplied with the outputs of the first and the second adders, for calculating the filter coefficients of the adaptive filter to compensate the transfer characteristics and supplying the calculated coefficient to the adaptive filter.
Moreover, the shaking table includes first and second bandpass filters having the same characteristics whose pass band is the same range as the compensated frequency range wherein the second command signal or the reference signal generator output is filtered by the first bandpass filter and then is added to the mask signal by the first adder, while the response signal is filtered by the second bandpass filter and is added to the mask signal by the second adder.
Moreover, in the aforementioned shaking table, the mask signal generator has a white noise generator and a bandstop filter for preventing the frequency band to be compensated by the adaptive filter.
According to another aspect of the present invention, there is provided an adaptive control device for controlling so that control state variables of a process to be controlled are agreed with a target signal, the device including:
an adaptive filter having variable filter coefficients which is supplied with the target signal and generating the control input signal, so as to compensate the transfer characteristics from the control input signal to the control state variable of the process to be controlled;
a signal generator for generating a mask signal having no frequency component in the frequency band compensated by the adaptive filter;
a first bandpass filter whose pass band is the same as the frequency band compensated by the adaptive filter and which is supplied with the control input signal;
a first adder for adding the mask signal to the output from the first bandpass filter;
a second bandpass filter having the same characteristics as the first bandpass filter, which is supplied with a control state variable calculated by a measurement unit;
a second adder for adding the mask signal to the output from the second bandpass filter; and
an identification unit which is supplied with the outputs of the first and second adders for calculating filter coefficients of the adaptive filter to compensate the transfer characteristics and supplying the calculated coefficients to the adaptive filter.